Dolastatin-10 was isolated from the Indian Ocean sea hare Dolabella auricularia in 1987 and identified to have the following chemical structure [J. Am. Chem. Soc., 1987, 109, 6883-6885]. Dolastatin-10 exhibits physiological activity as an antimicrotuble agent similar to taxane and vinca alkaloid, but is a structurally different peptide [Chem. Ind., 1999, 51-55; Curr. Pharm. Des., 1999, 5, 139-162].

Different in structure from taxane and vinca alkaloid as well as proven to have inhibitory activity against various human tumors in in vitro and animal model experiments in pre-clinical trials, dolastatin-10 was expected to not exhibit the side effects found in taxane and vinca alkaloid, such as myelotoxicity. In spite of the structural difference, however, dolastatin-10 was found to have myelotoxicity, neurotoxicity, and other side effects, such as taxane and vinca alkaloid, in clinical studies [Clin. Cancer Res., 2000, 6, 1293-1301; Drugs of the Future, 1999, 24(4), 404-409].
A variety of dolastatin-10 derivatives were synthesized, with derivatization conducted on the five moieties Dov (dolavaline), Val (valine), dolaisoleucine, dolaproline, and dolaamine. Of them, the dolaproline and dolaamine moieties have been intensively studied while dolastatin-10 derivatives were disclosed in WO 2003/008378 where the methoxy of the dolaproline moiety was substituted with thiomethoxy and in U.S. Pat. No. 5,599,902 where the dolaamine moiety was modified. Meanwhile, EP No. 260 858 discloses a derivative in which the dimethylvaline of the Dov moiety is substituted with monomethylvaline.